Brake squeal noise has been under investigation by automotive manufacturers for decades due to consistent customer complaints and high warranty costs. Sound in a squealing brake is excited by the contact between pads and the disc. It is well known that the material friction pad consists of several components making it a heterogeneous material. It is also well known that a part of the wear particles agglomerate at the surface leading to non uniform contact properties. The aim of this paper is to investigate the effect of heterogeneities of the friction material on the dynamic behavior of the brake. For this, an analytical model with three degrees of freedom (a translation and a rotation for the pad and a translation for the disc) has been developed including friction at the disc-pad surface contact surface. This model is computed with a complex modal analysis determining the frequencies of the system which can be coalesced to lead to mode lock-in which may be associated to squeal occurrence. The heterogeneities are introduced in the material properties. The results are compared to uniform material and contact properties, which are generally assumed in the literature. They show clearly that the distribution of these heterogeneities play a key role for the appearance of mode lock-in.